1. Field of the Invention
The invention relates to a signal amplification method, in which a difference between a reference signal, having different level heights, and a return signal, attenuated by feedback attenuation, of an output signal path is amplified by a servo gain path.
The invention relates further to an amplifier array with a servo amplifier, which has a reference signal input, a return signal input, and an output signal connection, which supplies an output signal path, a reference signal generator, which supplies reference signals with different level heights to the reference signal input, and with a return, which supplies a signal, attenuated by a value of the feedback attenuation, from the output path as a return signal to the return signal input, whereby the difference amplifier supplies an amplified difference between the reference signal and return signal in the output signal path.
In this regard, the term servo gain describes a gain that is substantially greater than the value one.
2. Description of the Background Art
A signal amplification method of this type and an amplifier array of this type are known from DE 198 23 096 A1, which corresponds to U.S. Pat. No. 6,166,597, and are used, for example, to operate a laser diode for CD and/or DVD devices. During the read operation (read), the laser diode is operated with direct current, on which a high-frequency signal is superimposed. The high-frequency signal reduces noise effects of the laser diode, but basically causes unwanted spurious emission. As a remedy, the noise effects are additionally suppressed by a relatively high bandwidth of the loop gain of a loop closed by optical feedback. Because of the additional suppression of noise effects by the high bandwidth, the amplitude of the high-frequency signal and thereby the unwanted spurious emission can be kept relatively low. In erase and write operations, the output signal, which is represented in this application by the emitted optical power of the laser diode, follows a reference signal, which serves as the input signal for the amplification. In this regard, during the erase operation and during the write operation, different high optical powers are necessary, which are generated by variably high levels of the reference signal. The write operation as a rule requires the highest optical power. Depending on the write/read strategy, any desirable high level can be necessary or favorable.
In general, steep edges of the current pulses are desired, with which the laser diodes are controlled. DE 198 23 096 deals with a loop gain, and which, on the one hand, is to be as high as possible, but on the other, may not lead to instabilities. In this regard, the loop gain is understood to be the total gain active in the loop. In DE 198 23 096, it is proposed in this context to control the loop gain and thereby to allow the actual value of a controlled variable (e.g., the laser diode optical power) during a pulse-shaped change of a command variable (e.g., of the reference signal) to overshoot the setpoint value by a preset tolerance value.
A basic problem here is that rapid changes within a time span, as are necessary for steep pulse edges, proceed with a large bandwidth in the frequency range. The limited bandwidth of control loop components therefore leads to an unwanted limitation of the edge steepness, which, for example, is obstructive to a fast write speed.